X-ray Spectroscopy Scanning Transmission Electron Research Articles

Biology in its Element: Using Energy Dispersive X-ray Spectroscopy Scanning Transmission Electron Microscopy (EDX-STEM) to Probe Bacterial Ultrastructure

Biology in its Element: Using Energy Dispersive X-ray Spectroscopy Scanning Transmission Electron Microscopy (EDX-STEM) to Probe Bacterial Ultrastructure

Effect of indium alloying on the charge carrier dynamics of thick-shell InP/ZnSe quantum dots.

Thick-shell InP/ZnSe III-V/II-VI quantum dots (QDs) were synthesized with two distinct interfaces between the InP core and ZnSe shell: alloy and core/shell. Despite sharing similar optical properties in the spectral domain, these two QD systems have differing amounts of indium incorporation in the shell as determined by high-resolution energy-dispersive x-ray spectroscopy scanning transmission electron microscopy. Ultrafast fluorescence upconversion spectroscopy was used to probe the charge carrier dynamics of these two systems and shows substantial charge carrier trapping in both systems that prevents radiative recombination and reduces the photoluminescence quantum yield. The alloy and core/shell QDs show slight differences in the extent of charge carrier localization with more extensive trapping observed in the alloy nanocrystals. Despite the ability to grow a thick shell, structural defects caused by III-V/II-VI charge carrier imbalances still need to be mitigated to further improve InP QDs.

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

AlxGa1-xN layers with Al-composition above 0.6 (0.6 < x < 0.9) grown under metal-rich conditions by plasma-assisted molecular beam epitaxy on m-plane GaN miscut towards the -c axis are kinetically unstable. Even under excess Ga flux, the effective growth rate of AlGaN is drastically reduced, likely due to suppression of Ga-N dimer incorporation. The defect structure generated during these growth conditions is studied with energy dispersive x-ray spectroscopy scanning transmission electron microscopy as a function of Al flux. The AlGaN growth results in the formation of thin Al(Ga)N layers with Al-composition higher than expected and lower Al-composition AlGaN islands. The AlGaN islands have a flat top and are elongated along the c-axis (i.e., stripe-like shape). Possible mechanisms for the observed experimental results are discussed. Our data are consistent with a model in which Al-N dimers promote release of Ga-N dimers from the m-plane surface.

ＲＥＢａ２Ｃｕ３Ｏ７−δ膜中ナノロッド形成におけるペロブスカイト構造―自己ペロブスカイト構造化―

Cubic perovskite structure has been found to play an important role for the nano-rod formation in REBa2Cu3O7-δ films. BaWO4,with a sheelite structure, and BaNb2O6, with a tungsten bronze structure, were doped into REBa2Cu3O7-δ targets. Laser-deposited, these materials formnano-rods in REBa2Cu3O7-δ films accompanied by Ln elements, resulting in the composition of a pseudo-cubic perovskite structure. This was confirmed by selected area electron diffraction patterns (SADP) and composition mapping using energy-dispersive X-ray spectroscopy scanning transmission electron microscope (EDS-STEM) analysis. BaWO4 with a sheelite structure, and BaNb2O6 with a tungsten bronze structure, doped into targets no longer retain their structures, but canform pseudo-cubic perovskite structures in laser-deposited REBa2Cu3O7-δ films. The perovskite crystal structure is thought to beimportant for nano-rod formation in the laser deposited REBa2Cu3O7-δ film.